Audio equipment such as a headphone or an earphone is equipped with a so-called noise canceling system for reducing external noise. For example, Patent Literature 1 discloses a headphone that has a noise cancellation function and a monitor function of outputting an audio signal of an external sound (a so-called monitor signal) to be superimposed on a musical signal and enables a user to listen to an external sound such as an in-vehicle announcement while obtaining a noise reduction effect for the musical signal.